STIG: Enforce Account & Password Policy

Bring this host's password policy to the DISA STIG baseline. In /etc/login.defs set a 60-day maximum password age, a 1-day minimum age, and a 7-day change warning. In /etc/security/pwquality.conf require a minimum length of 15 and at least one digit (dcredit -1). Grading reads the policy files the way a SCAP scan does. (Values are the Canonical Ubuntu 22.04 STIG's.)